calculate moving average of an integer over 10 values.

int moving_average(int a) {
  static int values[10] = {0};
  static int index = 0;
  
  values[index] = a;
  int sum = 0;
  for (int i = 0; i < 10; ++i) {
    sum += values[i];
  }
  index = (index + 1) % 10;
  return sum / 10;
}

moving_average(1); // 1
moving_average(2); // (1 + 2) / 2
moving_average(3); // (1 + 2 + 3) / 3
...